Recently, digital recording apparatuses such as a digital VTR, MD (Mini-Disc (a trademark)) recording and reproducing apparatus have been becoming widely used. Further, a DVD (Digital Videodisc (a trademark) or Digital Versatile Disc) have appeared and are installed in equipments such as a personal computer (PC).
As for such digital information recording apparatuses, it may be even easy to duplicate data or contents in a digital format or to alter them, thus the data and contents may be so unguarded as to be exposed to the risk of copyright infringement. Thus, it is not considered to be sufficient to simply tighten copyright laws and other laws and regulations relating to duplication, and in view of information technology it is considered to be necessary to support right use of data and contents or exclude fraudulent use thereof, thereby promoting copyright protection.
For example, for the purpose of protecting copyrights of digital music, major record companies in the United States took a central role in establishing a forum called SDMI (Secure Digital Music Interactive) in 1998. In accordance with the SDMI, it is prohibited to externally output contents of a digital format without any protection on them, therefore, it is defined to be essential that data contents to be transmitted are protected in case a content is output from an audio reproducing player to a rendering apparatus such as a loud speaker and headphones or in case the contents are output to recording equipments such as a DVD-R drive, a personal computer (PC), for example, (that is, prohibition of “unprotected digital out”).
For example, in the SDMI a function of so-called “Screening” is defined as a gadget for protecting copyrights in a portable music reproducing player. The Screening is the gadget for checking whether a content may be copied on a memory recorder of a portable device (PD), and it has been agreed that an electronic watermark is employed. For example, The Screening may be applied by means of the electronic watermark so as to exclude fraudulently delivered contents and once (or permitted times) copied contents from further copying.
Such SDMI requirements are considered to be essential not only in the case of cable connection between portable equipments but also in the case of wireless interconnection between the equipments.
Recently, “Bluetooth™” which is a representative example of short distance radio communication has been becoming widely used and installed in a variety of information equipments. The Bluetooth is a standard which provides a wireless connection interface applicable to a variety of fields, and “Bluetooth SIG (Special Interest Group)” has an authority to administer and manage the standard.
The Bluetooth uses a global radio frequency referred to as ISM (Industry Science Medical) band of 2.4 GHz and provides a general data transmission rate of 1 Mbps in which a synchronous transmission channel of 64 kbps applicable to voice transmission of telephone and an asynchronous transmission channel for data transmission.
The former synchronous transmission channel employs an SCO (Synchronous Connection Oriented Link) transmission system and is applied to interconnection between lines. And the latter asynchronous transmission channel employs an ACL (Asynchronous Connection Less Link) transmission system and is applied to data transmission by packet switching. A connection range between equipments through the Bluetooth is about 10 m and may be extended up to 100 m by using additional amplifier.
Technical specifications of the Bluetooth are generally classified into “Core” and “Profile.” The Core defines a base of wireless interconnection provided by the Bluetooth. Whereas, the Profile is a group of technical requirements which are defined for respective functions to ensure interconnectivity between equipments when different functions or applications developed based on the Bluetooth are installed in the equipments.
There are a plurality of Profiles in the Bluetooth which are combined to provide a single application (also referred to as an usage model (Usage)). In practice, a combination of profiles providing the application is mounted in a Bluetooth product together with the Core.
For example, a variety of Bluetooth Profiles such as those concerning a cellular phone and a personal computer and further concerning an automobile, a network, a printer, audio, video, etc. may be assumed.
For example, as a Profile for transmitting audio data, “Bluetooth Advanced Audio Distribution Protocol” (A2DP) may be quoted. According to this Profile, wireless interconnection between an AV reproducing equipment and rendering apparatus such as a loud speaker or headphones and wireless connection between the AV reproducing equipment and a rendering apparatus such as a DVD-R drive or a personal computer (PC) may be achieved.
In such an AV equipment equipped with the Bluetooth, in order to comply with the above-mentioned SDMI, there is a need for equipping a gadget for prohibiting “unprotected digital out” or a gadget for protecting an audio data to be digitally transmitted.
The Bluetooth security basically sets a common parameter referred to as “Link Key” between specific two terminals, and one-to-one security is managed between a master and each slave (its link key is not disclosed to a third party).
Elements for protecting digital data are generally classified into two, which are encryption for preventing “wiretapping (eavesdropping)” and authentication for preventing “spoofing.”
Since the Bluetooth SIG is not involved in protection systems of contents, each vendor has to protect contents on its hands. However, an authentication system between audio equipments equipped with the Bluetooth must be provided not in a Bluetooth layer but in the application layer which is higher than the former.
The present inventors consider that protection gadgets are different between the use of the Bluetooth communication for rendering (or just listening to) such as headphones and a speaker and the use of the communication for recording.
As for recording, as in the case of Music Download, it is often the case that sufficiently satisfactory protection of high intensity level is applied to each application.
Whereas, as for the rendering, it is unlikely to define how much the intensity should be. It is difficult to require or necessitate the protection of high level for equipments equipped with a CPU of low processing power such as headphones, for example.
In order to apply full authentication of a DTCP (Digital Transmission Content Protection) which is a copy protection standard for i-LINK (IEEE 1394), for example, a load of operating time of about 600 ms is necessary by computing with a CPU of MIPS R4000 100 MHz. It is not practical to impose such cost of a CPU or processing time on terminal portable equipments such as headphones. Further, in a portable equipment based on a battery drive, power consumption can be a problem with system design, and it is difficult to uniformly employ an authentication system of such an overlade level.
On the other hand, a personal computer (PC) equipped with recording function must be prevented from recording fraudulently by pretending to be for rendering.
When an authentication system using 8-bit key, for example, is employed as a rendering use in order to be easily applied to an equipment of lower operating power such as headphones, it may be easily broken by a personal computer of high operating power, thereby reducing effects of its protection.